Lopez saved four set points in the tiebreaker before jumping to a 4-0 lead in the second set and firing an ace to clinch victory.

The Spanish lefty will next play eighth-seeded Gael Monfils of France.

Nishikori got a cold dose of reality after stunning Djokovic last weekend to reach the final of the Swiss Indoors in Basel. He could only convert two of 14 break chances against Stakhovsky, who won to set up a clash with Viktor Troicki of Serbia.